This invention relates to pneumatic tires and more particularly to a novel and improved tire cord fabric and the use thereof in a pneumatic tire to reduce defects in tires known as blows.
In the curing of a pneumatic tire the presence of air or other compressible gases within the body of the tire being cured may cause defects which are known as blows or blisters. These defects may involve local separation between the rubber and one or more of the reinforcement cords which make up the reinforcing ply of a pneumatic tire. Air may become trapped in or between the layers of materials which are superimposed in the course of building the tire or may in some instances enter into the tire during the time lapse between the building of the tire and the placing of the tire into a mold in which it will be cured. Occasionally small quantities of air may be forced into the body of the tire by the closing of the mold.
It has been known in the art that tire reinforcement cords contain passages extending generally throughout the length of the cord, lying between and bounded by the filaments which make up the cords, and that air or other gases can travel along such passages. It has been observed that the treatment of tire reinforcement cords such as stretching of heated cords, for example cords made of continuous synthetic resin filament materials such as polyester and nylon, tends to significantly reduce the cross sectional area of the interfilamentary passages. Stretching of heated cords may result in a reduction of a cross sectional area of the individual filaments and a compacting of the filaments more closely to one another.
During the time that the tire is being vulcanized by the application of heat and pressure thereto, any air trapped within the tire or any gases generated during the vulcanization of the tire may be sufficient in volume to prevent the development of a satisfactory bond between the rubber material and the reinforcing cords within the tire or may break such bonds by forcing a separation between the rubber and the reinforcement cords. The resulting defects are known as blisters or blows. Examples of attempts to minimize such blisters or blows are described in U.S. Pat. Nos. 2,541,506, 3,552,468 and 4,363,346.